At present, hydrophilic fibers (e.g. pulp) and water-absorbent resins which are water-swellable crosslinked polymers as obtained from such as an acrylic acid (salt) as a major raw material, are widely utilized as constituent materials of sanitary materials, such as disposable diapers, sanitary napkins, and so-called incontinent pads, for the purpose of causing them to absorb body fluids. In recent years, these sanitary materials such as disposable diapers, and sanitary napkins improve in high function and thinning. The amount of the water-absorbent resin as used per one sanitary material sheet and the weight ratio of the water-absorbent resin relative to the entire absorbent structure including such as the water-absorbent resin and the hydrophilic fiber tend to increase. In short, the ratio of the water-absorbent resin in the absorbent structure is increased by making the amount of the hydrophilic fiber having a small bulk density decrease, and by using the water-absorbent resin having excellent water absorbency and a large bulk density in a large amount. Thereby, the thinning of the sanitary material is attempted without lowering the water absorption quantity.
However, the above matter is a favorable course, from the viewpoint such that: the ratio of the hydrophilic fiber is lowered in such a manner; and the sanitary material in which the amount of the water-absorbent resin is increased simply stores a liquid, but on the contrary, it causes problems when the distribution and diffusion of the liquid are thought in a circumstance of practically using diapers. The water-absorbent resin in a large amount becomes a soft gel due to absorbing water. Therefore, caused is so-called gel blocking, which is a phenomenon such that the diffusion of liquids is greatly hindered. In order to avoid such a problem and to maintain the absorption performance of the absorbent structure, the ratio between the hydrophilic fiber and the water-absorbent resin is naturally limited, and the limitation of thinning the sanitary material is also caused.
In order to enhance the diffusion of the liquid in the absorbent structure and to use an absorbent material more efficiently, methods for distributing and diffusing a liquid, or liquid-diffusing members have hitherto been variously considered, and absorbent articles including these members have been variously known. Examples of these include: an absorbent pad in which a specific region of a hydrophilic fiber in an absorbent structure is compressed in a high density (U.S. Pat. No. 4,781,710); a liquid-distributing material having specific suction properties, which is obtained by molding and combining at least two kinds of fibers having different strength and specific surface area in a wet condition (WO 97/45087); a form-type absorbent material having continuous foam, which is produced by using a high-internal-phase emulsion (U.S. Pat. No. 5,387,207, U.S. Pat. No. 5,134,007, and U.S. Pat. No. 6,107,538); and an absorbent core, which favorably has a narrow crotch width including a form-type absorbent material having continuous foam and in which the absorption ability of the crotch region is not more than 40% of that of the entire absorption ability of the absorbent core (WO 98/43573 and JP-A-510365/2000).
In addition, members for acquiring liquids have been proposed in order to enhance liquid absorption efficiency and liquid retention of an absorbent article such as a disposable diaper. Known examples of such a liquid-acquiring member include: crosslinked cellulose (JP-A-264971/1988); and an exhaust-treating layer having a specific liquid permeation ratio index (JP-A-261126/1993).
However, it was made clear that: when the water-absorbent resin is used as a storing material in order to store the liquid as distributed and diffused by the above liquid-diffusing member, depending upon the liquid-diffusing member as used, the liquid therein is hardly transferred and absorbed to the water-absorbent resin, and the water-absorbent resin does not work efficiently as the liquid-storing member. It was made clear that: when especially a material having very high suction ability in the vertical direction, such as a porous polymer which is produced by using the high-internal-phase emulsion as mentioned above and has fine continuous foam therein, is used as the liquid-diffusing member, surprisingly, depending upon its properties, there are cases where the water-absorbent resin can hardly absorb the liquid from the above porous polymer and where the original storing function of the water-absorbent resin can hardly be displayed. Accordingly, even if the liquid can be diffused in the absorbent structure sufficiently, the function of storing it does not work favorably. Therefore, found was the phenomenon such that the leakage of the liquid from the absorbent article is caused with a far less capacity than an expected absorption quantity.
As to the arts to solve this problem, WO 99/47184 and U.S. Pat. No. 6,107,538 disclose a liquid-storing member having high capillary absorption ability, which is obtained by combining an absorbent material due to osmotic pressure (e.g. the above water-absorbent resin) with a material having a large surface area (e.g. a particulate porous-foam-type absorbent material which is produced by using the above high-internal-phase emulsion and has continuous foam, and a glass micro fiber).
However, according to this method, at least two materials as mentioned above are combined and used as the liquid-storing member. Therefore, a new apparatus for combining these materials in order to produce the liquid-storing material is necessary, and the steps are complicated, and besides, there is a problem such that the absorption ability of the water-absorbent resin is yet still in a low level even if there is a material having a large surface area around the water-absorbent resin. When the absorption ability of the material having a large surface area as used further is lower than that of the water-absorbent resin, there is also a problem of lowering the liquid absorption and storage ability of the entire liquid-storing member.
In addition, as is aforementioned, the liquid is rapidly captured into the absorbent structure in an initial state by making the liquid-acquiring member to exist. However, as the absorption quantity is increased, there were found cases where: since a certain time, the absorbent structure including such as the water-absorbent resin and the hydrophilic fiber cannot absorb the liquid in the liquid-acquiring member, and the absorption rate becomes slow conversely, and the amount of wet back of the aqueous liquid is increased.
In addition, as to even an absorbent article called as thin-type one at the present circumstances, the weight thereof is yet still heavy, and the thickness thereof is thick. Therefore, it is yet still unsatisfactory for such as circulation of goods, displaying space, purchase, and outdoor use, and further thinning is requested. Accordingly, when the concentration of the water-absorbent resin in the absorbent structure was further increased, for example, when the amount of the bulky hydrophilic fiber as used was decreased and a water-absorbent resin layer including the water-absorbent resin in a major proportion was tried and used as the liquid-storing member, there were cases where: the problem of the gel blocking of the water-absorbent resin as aforementioned draws attention more, and the objective absorption capacity cannot be realized.
Known examples of arts of using the water-absorbent resin layer including the water-absorbent resin in a major proportion as the liquid-storing member include: an absorbent core as equipped with a first structure and a second structure, wherein the first structure includes a first fiber material and a first super-absorbent material, and wherein the second structure includes a second fiber material and a second super-absorbent material of which the absorption rate is faster than that of the first super-absorbent material (JP-A-511973/1996); an absorbent structure having an upper constituted structure and a lower constituted structure having a special structure, wherein the upper constituted structure includes a liquid-capturing layer and a super-absorbent material layer that is comprised of a super-absorbent material having a gel layer permeation value of not less than a specific amount, and wherein the lower constituted structure includes an upper layer having an opening space for storing a liquid, and a lower layer storing a super-absorbent material layer of which the absorption capacity is in a specific range under a load (JP-A-511974/1996); an absorbent article including a first absorbent layer and a second absorbent layer, wherein the first absorbent layer in which a water-absorbent polymer is retained between nonwoven-fabric-made fibers, and wherein the second absorbent layer is comprised of a hydrophilic fiber aggregate, and wherein the first absorbent layer is located at the side of a liquid-permeable surface sheet (JP-A-286505/2001); and an absorbent structure, which is an absorbent structure including a humidable fiber and a surface-crosslinked water-absorbent resin and having no gel blocking property, wherein the weight ratio of the water-absorbent resin is in the range of 75 to 95 weight % relative to the, fiber and the above surface-crosslinked water-absorbent resin, and wherein the ratio of volume as increased is not less than 15% after 600 seconds under a load (WO 01/30290).
In these above JP-A-511973/1996 and JP-A-511974/1996, disclosed are the art relating to the constitution of the absorbent structure, in which the liquid-storing position in the absorbent structure is transferred from downward to upward. In JP-A-286505/2000, disclosed is the art in which the roughness of a back sheet in a diaper is removed. In WO 01/30290, disclosed is the art in which the opening ratio of the absorbent structure in a swollen state is defined. However, the distribution relationship of the liquid between the liquid-acquiring member and the water-absorbent resin layer that catch the liquid is not mentioned.
In addition, also filed was the art relating to a absorbent article for body fluids, in which the water-absorbent resin ratio is in the range of 10 to 90 weight % relative to the total amount of a pulp and a water-absorbent resin, wherein a water-absorbent polymer having specific performance for aspirating and sucking body fluids is used in order to transfer a liquid as retained in a pulp fiber space into the polymer (JP-A-276124/2001).
However, the polymer as used in this case is a polymer having a comparatively small bulk density and a high unshaping degree, and the so-called absorption rate of rapidly absorbing the liquid as retained in the pulp space around the polymer is regarded as an important matter, and similarly the distribution relationship of the liquid between the liquid-acquiring member and the water-absorbent resin layer is not disclosed.